The secondary battery is composed of a negative electrode, a positive electrode, an electrolyte and a current collector. A reduction reaction by electrons generated from the negative electrode occurs in the positive electrode, and the current collector serves to supply a positive active material with electrons generated from the negative electrode on discharging the battery or supply a negative active material with electrons supplied from the positive electrode on charging the battery.
As the sodium secondary battery uses sodium rich on earth, it has an excellent competitiveness in terms of a material supply-demand property and a manufacturing cost and an advantage to be capable of making high capacity battery with a simple structure compared to a lithium ion battery.
Moreover, in order to manufacture a sodium secondary battery having an excellent charge and discharge capacity, a material having high electrical conductivity has to be used as an electrode material. However, since NaTi2(PO4)3 being used as a negative active material of the conventional sodium electrode has a low electrical conductivity to be not smooth supply of electrons, which acts as a factor to inhibit the electrode efficiency. Therefore, it is urgently required to develop a technique for enhancing the electrical conductivity of the negative active material.